PM Update: Cold front brings winter back

Freezing Friday before potential weekend snow event

Today's warmth is about to become a memory as a cold front pushes through and sends us back into the freezer. Highs managed to top 50 most spots this afternoon, climbing as high as the mid-50s in some places. Significant temperature drops are about to occur though and tonight and tomorrow will be much colder before a snow threat, which has already prompted Winter Storm Watches to our south, for late Friday night and Saturday.

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Through Tonight: Despite today's warmth, we'll head right back into midwinter chill overnight as frigid air rushes back into the area behind the cold front. Lows should tumble into the teens in many of the suburbs to perhaps the lower 20s downtown. Winds will be quite gusty too, especially early.

Tomorrow (Friday): It's going to be a cold one tomorrow, especially compared to today. On the bright side, we'll see a fair amount of sun thanks to a slower potential snow event than initially suggested. Partly sunny skies won't do much to warm things though as temperatures rise into the upper 20s and lower 30s for highs.

Midday model update: The storm system initially scheduled to arrive tomorrow has been a tricky one to forecast thus far. The timing has slowed, and the precipitation forecast has vacillated in just about every way imaginable. For snow lovers, the trends today have again been "good" as the northern edge of precipitation has shifted north with most if not all model guidance. Since the system has slowed down a bit, we still have plenty of time for small shifts. We're sticking with the accumulation probabilities we mentioned earlier today for now, but stay with us to learn the latest as it becomes available.

Have a question for CWG - I get pretty irritated when people say "we definitely won't get another snow storm this year, because we already had a big one in December." This bothers me because logically how can that be? I would guess that two snow storms are somewhat independent of each other, and if their occurrence is in any way tied together, it would be positively. Such that if we already had a big snow storm, many factors might be place that would raise probability of another one (such as a negatively tilting arctic oscillation). The idea of having one big snow storm lowering the chances of having another big snow storm is like saying the "snow gods" already gave us our "snow allotment" this year, so none is left for another storm. (Which obviously is ridiculous) I say all this also realizing that the probability of another storm like the one in December is fairly low, but the chances are NOT less slim just because we already had a storm. Thoughts? Does this make sense?

Chance of snow for Fairfax up to 80% (From the National Weather Service) - about 15 miles due south in Lake Ridge - 100%..

A WINTER STORM WATCH HAS BEEN ISSUED FOR PORTIONS OF THE VIRGINIA
PIEDMONT FOR OVERNIGHT FRIDAY THROUGH SATURDAY EVENING. PLEASE
REFER TO WSWLWX FOR FURTHER DETAILS. ACCUMULATING SNOW IS LIKELY
DURING THIS TIME ACROSS THE WASHINGTON METROPOLITAN AREA.

The NCEP Short Range Ensemble Forecast system (SREF) brings the 50% chance of 2-4" just about up to DC, with 30% chance of 4-8". But the north to south gradient of probabilities is large, so a very small - and unpredictable at this time - shift in storm track can make the difference between no snow at all in DC Metro region to a moderate snowfall.

Stay tuned - if it were reasonably possible now to be more confident one way or the other, I'm sure CWG would be on top of the story. But, that's just the way it is with weather - some events are more predictable than others, and acknowledging this is critical in conveying the best information possible.

This is because most people have little understanding of probability. Try this - ask people "if you flip a coin 10 times and get heads every time, what is the chance of getting heads on the 11th flip" and see what they say.

The odds of every coin toss is 50/50, the probablitity changes with every toss. The odds never change but the probability does. The probability that the 11th toss will b tails is greater, but the odds r always 50/50. That being said, their is no correlation 1 storm & the next.

@jahutch and @VaTechBob - this is exactly what I mean - it is the law of independent probabilities. BUT I do think two snow events in one season are not completely independent of one another. The only correlation would have to be positive though - not negative - see my above post. I guess I'm harping on a minor point that I just get tired of hearing from people.

so madison and greene county va is not part of the watch?? i dont get the warning maps somtimes. how is it, if you look at the map, greene is just as south as orange county and madison is even with orange. i dont get how, especially greene county, is not part of the watch. when just due west there is a watch area. its as if greene is magically going to be missed.

For a winter storm watch there has to be an expectation of 5 or more inches of snow (or a quarter inch of ice). Since the entire area is right on the cusp of this thing, and they have to draw a line SOMEWHERE, it looks like Orange and Madison-Greene is where that somewhere is. If they are expecting closer to 4 inches in Madison and Greene, look for a winter weather advisory a little closer to the outset of the storm....

I just watched John Bernier's lead off on WRIC Channel 8. Predicted a band of 12-16+ for Danville and southernmost VA. A bit less for Richmond. Fredricksburg was shown as 3-6. His map didn't go up far enough to show DC.

CM_in_Fairfax, the probability of flipping a fair coin 10 times and getting heads every time is 1/2^10 = 1/1024 (or 1 in 1024). You have a better chance of this than winning the powerball lotto grand prize (1/195249054).

Also, VATechBob, if the coin is fair, then each flip of the coin is independent and the probability of the 11th toss being a heads or a tails does NOT "depend" on the prior results.